Added test cases to test plan, edited medium setup

New test cases:
* data server restart
* data server restart while downloading files (draft)
* write conflict
* restart first proxy, wait until it starts, restart second proxy
* ring builder and rebalancing
* different time zones between regions
* proxy affinity

Edited medium setup, since the third data server is unnecessary and keystone
should be on a separate server to test proxy server restarts.

Fixed minor issues with other test cases and clarified a few points.